Full exhausts to open headers gain

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Hot Metal

Hot Metal

'69 440 Cuda
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We have a 3800lb car that currently runs a mild street/strip BIG wedge motor, best this year so far were 10.3's@129-ish, has gone best of 130 with full exhausts. It has 2.18>2.14" TTI step hdrs 4" collector with 2.5" pipes to the rear, not sure on the muffler make. The heads are -13's 365CNC, cam is small s/roller with 260/270@.050 and runs a good working but small 950HP carb. Stall is 4200-ish with 4400 being max torque on motor, car hooks and goes 1.43 60's best to date with caltracs/mono's.
Apart from the weight (50lbs?) loss have any of you run with exhausts and gone open, if so what was your gain and what can be expected on our set up with info given, whats your estimates guys, up jetting of course will prob be needed....bit of a how long is a piece of string question but lets see what you say.
 
That big collector needs to be 20 inches long at least if you drop the exhaust. Probably longer than that.
 
Don't forget the added weight of some earplugs LOL... Probably worth 1/10 or 2.... Is it worth it? That's the question...
 
I don’t recall the details for pretty much all the combos where I’ve seen that tested....... but I do remember one.

SBC 406”, 13:1, roller cam, single plane, too small headers for this motor(1-3/4), 5000 stall, glide, 4.30’s w-28” slicks, in a 65 Nova.
Mid-10 second car.
The exhaust system was 3” pipe to 3” flowmasters, with the pipes exiting in front of the rear tires.
Removing the exhaust and installing collector extensions was worth almost .3 and over 2mph.

Most of the loss with the exhaust I attributed to the flowmasters.

In your case, it’s really just a matter of...... try it and see...... then iiwii.
No point in overthinking it.
 
Not overthinking it as its prob not going to happen anyway, just a topic of conversation, I personally would like to see the car get as close to a street driven 9 sec car as poss with the current combo, that would go someway towards "my" personal goal for the car, but not necessarily the owners unfortunately, its "Free" 10ths for no money as opposed to a $1000 for a carb that may only gain a 10th so why not try it, to me a race car is not that unless it sounds like one and it would help our brkt racing in my opinion if we were more on a par with the other cars that go rounds that run in the 10.0's high 9's.
 
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Ha!
I was just reading a road test last night from the Dec 1968 issue of Hot Rod magazine.
1969 A56 3.91 E70x14 Polyglas 340'cuda. Stock except Hooker fenderwell headers through factory pipes/mufflers, ignition recurve, Edelbrock intake and Holley carb. You can bet it was tuned by someone at Chrysler.

Anyway, with Ronnie Sox rowing the 4 speed at Irwindale, his best time was 13.33 at 106.5 mph with open headers. With exhaust hooked up times increased to 13.70s. Test weight 3520 lbs.

I'm no expert, but 2-1/2" pipes on your car is too small if you insist on runnning full exhaust.

20201218_120252.jpg
 
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It's been 10-15 yeas ago, but after several years of tuning my 360 Dart Sport with TTI stepped headers and long collectors, I switched to a 3" X-pipe ending with Dynomax Ultraflos at the rear housing. It picked up a bit, then a bit more after I jetted down 2 #'s. The weight of the exhaust was removed from elsewhere in the car to keep that factor consistent. I don't think it was over a tenth, but for class racing it was certainly worth keeping it on and my ears liked it too! (Mid-low 11's up to 118 mph @ 3,550+ lbs.)
 
I have always raced with mufflers, and my local tracks now require them (tho i cant say that i have seen them rigorously enforce the rule), so i dont have personal experience. However i agree with above, that you will need collector extensions, and 2 1/2 is WAY small for 600". I would not be a bit surprised to see you pick up two tenths/three mph, after re-jet. I've used 2"headers, 3 1/2 mufflers and exhaust on a nine second street small block (granted, at a LOT less weight than you).

Edit: if it doesnt have an h pipe, or an x pipe, could you just move them sideways and use the collector bolts to hold the exhaust up, like we did in the old days? You wouldnt have to remove the exhaust system that way. Easy a to b test that way.
 
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Keep in mind that reality doesn't always match textbook. Sometimes they fall off with the exhaust removed. Especially if it's a really good system.
 
I personally would like to see the car get as close to a street driven 9 sec car as poss with the current combo
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“In theory”, to go from a 10.30 to a 9.95 @3900lbs, would require an increase of about 80hp.
 
PRH said:
“In theory”, to go from a 10.30 to a 9.95 @3900lbs, would require an increase of about 80hp.
Click to expand...

correct and thats not happening with just the exhausts removed@3800lbs, which is why I said "as close to" a 9 sec street driven car. "In theory" a 50lb weight loss is worth approx .04, just a 10th in ET for open hdrs and carb jetted right to be conservative which could bring it down to 10.20's....removal of the 4" drop air cleaner which I've not mentioned yet where we got .08 from last time out which could bring it down to 10.1's, from there it would be difficult to gain any more but these are all free mods surely its worth a shot at it, but we are not all of the same thinking unfortunately.
 
inertia said:
I was 2/10ths quicker uncapped .
Click to expand...

On a 72 vega w/ a fairly hot 406 sbc , and my home built mufflers /1 7/8 tube headers, I gained .003 of a second by dropping the 3'' system off , I think it was the weight diff. , I dont even take the 3 1/2'' system off or open it up on the fish.
 
I saw almost 50hp when we dropped the pipes on my Chevelle from the past..... But it was expected since it had Shorty headers and 2 1/2" exhaust to the bumpers which was not ideal for a 540. That was not so much as touching anything else but my friend who ran the Dyno knew it would be the biggest gain he would ever see from just that.....

JW
 
A 2.5" system with 589ci is SMALL, which is why I mentioned this, its the same exact system he ran with the mild 440 which was in the car previous. General consensus is a 2/10ths gain is poss which I would go along with, thats roughly 25>30hp which is just about how much we are off from the best dyno run which was 695 on the day>
695hp@3800lbs=
60 Foot E.T. : 1.43
1/8 Mile E.T. : 6.47
1/8 Mile Trap Speed : 104.98
1/4 Mile E.T. : 10.26
1/4 Mile Trap Speed : 131
1/4 Mile Trap RPM :
as we are only .09 off that currently and around 1 mph off corked up its reasonable to think that it could be a 10.1 car, and I believe there's still some in the chassis as it is, normally there always is...is it worth doing?.....hell yeah in my book, lets hope we get to try it next year....thanks for the replies.
 
My car picks up .1 and 1mph last I checked. Its a 550-600HP 416" small block. The full exhaust system is a muffler shop bent deal with ultraflow mufflers, 3" to the mufflers and 2.5" tailpipes.
 
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